JP2024067676A - Gas Separation Systems - Google Patents

Abstract

The present invention provides a gas separation system that can improve the recovery rate of a specific gas and supply gas with a reduced concentration of the specific gas to users who do not require the specific gas.
[Solution] A gas separation system is used which includes a first separation membrane module having a first gas separation membrane that selectively permeates a specific gas and which is separated into a primary side and a secondary side by the first gas separation membrane, a second separation membrane module having a second gas separation membrane that selectively permeates a specific gas and which is separated into a primary side and a secondary side by the second gas separation membrane, a first permeable gas pipe connected to the secondary side of the first separation membrane module, a second non-permeable gas pipe connected to the primary side of the second separation membrane module, a second permeable gas pipe provided between the secondary side of the second separation membrane module and the first supply pipe, which supplies gas that has permeated the second gas separation membrane to the first supply pipe, and a second branch pipe connecting the second supply pipe or the second non-permeable gas pipe to the secondary side of the second separation membrane module.
[Selected Figure] Figure 1

Description

This disclosure relates to a gas separation system.

As a method for separating a specific gas from a mixed gas containing multiple types of gases, there is a method that uses a separation membrane that selectively permeates gas. Separation membranes include, for example, molecular sieve membranes, which separate gases based on differences in molecular diameter, such as ceramic membranes, and polymer membranes, which utilize differences in the solubility of gases in the membrane. These separation membranes also allow a certain amount of gases other than the specific gas to be permeated. Here, the side before the gas is permeated through the separation membrane is called the "primary side," and the side after the gas is permeated through the separation membrane is called the "secondary side." The amount of gas permeated through the separation membrane is the difference between the gas partial pressure on the primary side and the gas partial pressure on the secondary side multiplied by the gas permeation rate and the membrane area. Polymer materials can be easily formed into hollow fibers to increase the membrane area, and modules that bundle hollow fibers of polymer membranes are commercially available. Gases that do not permeate the secondary side in the module are discharged from the module.

Patent document 1 discloses that an apparatus including a chain of three membrane separation processes and having a compressor installed on the supply side of the feed stream separation process can be used to supply a permeate stream and/or a concentrated stream that do not require further purification. It is also disclosed that in this apparatus, after the second permeate stream or the third concentrated stream is returned, the feed stream is composed of the gas of the crude gas stream, the gas of the second permeate stream, and the gas of the third concentrated stream.

Patent No. 5858992

In the device described in Patent Document 1, the specific gas that did not permeate the first module is permeated to the secondary side of the second module and then supplied to the first module again, and the gas that permeated the first module is permeated to the secondary side of the third module to increase the concentration of the specific gas, and the gas that did not permeate to the secondary side of the third module is also supplied to the first module again to improve the recovery rate.

The recovery rate can be further improved by reducing the amount of non-permeated specific gas discharged from the second module. In order to reduce the amount of specific gas discharged, it is possible to increase the amount of specific gas permeated through the first and second modules. Furthermore, in facilities that use natural gas, etc., where specific gas becomes an impurity, it is desirable to increase the amount of specific gas permeated and improve the concentration of non-permeated gas, such as natural gas.

The objective of this disclosure is to provide a gas separation system that can improve the recovery rate of a specific gas and supply gas with a reduced concentration of the specific gas to users who do not require the specific gas.

The gas separation system of the present disclosure includes a first separation membrane module having a first gas separation membrane that selectively permeates a specific gas and that is separated into a primary side and a secondary side by the first gas separation membrane, a second separation membrane module having a second gas separation membrane that selectively permeates a specific gas and that is separated into a primary side and a secondary side by the second gas separation membrane, a first supply pipe that supplies a mixed gas containing the specific gas to the primary side of the first separation membrane module, a second supply pipe that connects the primary side of the first separation membrane module and the primary side of the second separation membrane module, a first permeable gas pipe connected to the secondary side of the first separation membrane module, a second non-permeable gas pipe connected to the primary side of the second separation membrane module, a second permeable gas pipe provided between the secondary side of the second separation membrane module and the first supply pipe, that supplies gas that has permeated the second gas separation membrane to the first supply pipe, and a second branch pipe that connects the second supply pipe or the second non-permeable gas pipe to the secondary side of the second separation membrane module.

According to the present disclosure, it is possible to provide a gas separation system that can improve the recovery rate of a specific gas and supply a gas with a reduced concentration of the specific gas to users who do not require the specific gas.

1 is a schematic configuration diagram showing a gas separation system according to a first embodiment. FIG. 1 is a diagram showing the results of trial calculation of the gas separation performance of a gas separation system of a comparative example. FIG. 2 is a diagram showing the results of trial calculation of the gas separation performance of the gas separation system of FIG. 1. FIG. 2 is a schematic configuration diagram showing a gas separation system according to a second embodiment. FIG. 5 is a diagram showing the results of trial calculation of the gas separation performance of the gas separation system of FIG. 4. FIG. 11 is a schematic configuration diagram showing a gas separation system according to a third embodiment. FIG. 7 is a diagram showing the results of trial calculation of the gas separation performance of the gas separation system of FIG. 6. FIG. 13 is a diagram showing the results of trial calculation of the gas separation performance of a gas separation system according to a modified example of the third embodiment. FIG. 13 is a schematic diagram showing a gas separation system according to a fourth embodiment. 10 is a graph showing the results of a trial calculation of the relationship between the first dilution gas flow rate and the hydrogen concentration of the recovered gas, with the hydrogen concentration of the gas supplied from the first supply pipe being used as a parameter in the gas separation system of FIG. 9 . FIG. 13 is a schematic configuration diagram showing a gas separation system according to a fifth embodiment.

One embodiment of the present disclosure relates to a system that allows a specific gas user to separate and use the specific gas at a usage site when a specific gas different from natural gas is mixed with natural gas and supplied using an existing pipeline for natural gas, etc., or a system that allows the user to use natural gas, etc. from which the specific gas has been removed, and a system that purifies gas in a gas production facility, a chemical plant, etc. An example of a specific gas is hydrogen gas.

A gas separation system according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that, in the following, a case will be described in which the mixed gas contains methane, which is the main component of natural gas, and hydrogen, which is a specific gas. However, the gas separation system of the present disclosure is not limited to such a mixed gas composition, and is desirably applied to all cases in which both the specific gas and the residual gas (referred to as "non-permeable gas" in the following embodiments) remaining in the mixed gas side as a result of separating the specific gas are effectively utilized without being released (discharged) or disposed of outside the device. It is desirable that at least the specific gas is effectively utilized. Here, effective utilization can be rephrased as "useful."

Another example of a mixed gas is exhaust gas generated at power plants, factories, etc. Exhaust gas contains carbon dioxide generated by combustion, nitrogen, oxygen, etc. In this case, at least carbon dioxide is effectively used as a specific gas. Carbon dioxide is useful as a carbon source in organic synthesis.

[First embodiment]
In this embodiment, a case will be described in which hydrogen is separated from a mixed gas of hydrogen and methane by a hydrogen separation membrane and recovered on the secondary side.

Figure 1 is a schematic diagram showing the gas separation system of this embodiment.

In this figure, the hydrogen separation system 1 (gas separation system) is configured to receive a mixed gas of hydrogen and methane through a first supply pipe 3 branched from a main mixed gas pipe 2. The hydrogen separation system 1 has a first separation membrane module 11 and a second separation membrane module 12. The first separation membrane module 11 is separated into a primary side 33 and a secondary side 34 by a hydrogen separation membrane 15 (first gas separation membrane). The second separation membrane module 12 is separated into a primary side 43 and a secondary side 44 by a hydrogen separation membrane 16 (second gas separation membrane). The hydrogen separation membranes 15 and 16 selectively allow specific gases to pass through. The hydrogen separation membranes 15 and 16 are polyimide membranes, which are polymer membranes. Note that the hydrogen separation membranes 15 and 16 may be ceramic or carbon-based.

The first supply pipe 3 is connected to the primary side 33 of the first separation membrane module 11. The first supply pipe 3 is provided with a supply gas flow rate control valve 23. The second supply pipe 4 is provided between the primary side 33 of the first separation membrane module 11 and the primary side 43 of the second separation membrane module 12. The second non-permeate gas pipe 9 is connected to the primary side 43 of the second separation membrane module 12.

The first permeable gas pipe 5 is connected to the secondary side 34 of the first separation membrane module 11. The second permeable gas pipe 6 is connected to the secondary side 44 of the second separation membrane module 12. The second permeable gas pipe 6 is connected to the first supply pipe 3. The second permeable gas pipe 6 is provided with a booster 30.

The second supply pipe 4 is provided with a second branch pipe 7 (dilution gas pipe) and is connected to the secondary side 44. The second branch pipe 7 is provided with a second dilution gas flow control valve 24 and a pressure reducing valve 21. The second dilution gas flow control valve 24 may also perform the pressure reducing function, and the pressure reducing valve 21 may be omitted. Non-permeating gas flows out from the primary side 33 of the first separation membrane module 11 into the second supply pipe 4. A portion of this non-permeating gas flows into the secondary side 44 as the second dilution gas via the second branch pipe 7. The second dilution gas flow control valve 24, or the second dilution gas flow control valve 24 and the pressure reducing valve 21 are also referred to as the "second dilution gas flow control unit."

Of the mixed gas supplied from the mixed gas main pipe 2, mainly hydrogen permeates the hydrogen separation membranes 15, 16. Methane also permeates the hydrogen separation membranes 15, 16, but hydrogen permeates more easily than methane. For this reason, the secondary side 34 has a higher hydrogen concentration than the primary side 33. Similarly, the secondary side 44 has a higher hydrogen concentration than the primary side 43. The permeation amount of each gas through the hydrogen separation membrane 15 is calculated by multiplying the partial pressure difference of each gas between the primary side 33 and the secondary side 34, the permeation rate, and the membrane area of the hydrogen separation membrane 15. Similarly, the permeation amount of each gas through the hydrogen separation membrane 16 is calculated by multiplying the partial pressure difference of each gas between the primary side 43 and the secondary side 44, the permeation rate, and the membrane area of the hydrogen separation membrane 16.

The gas that has permeated the first separation membrane module 11 is recovered through the first permeation gas pipe 5 connected to the secondary side 34. The mixed gas (non-permeation gas) that has not permeated the first separation membrane module 11 is supplied to the second separation membrane module 12 through the second supply pipe 4. Since the second supply pipe 4 is branched by the second branch pipe 7 midway, the non-permeation gas of the first separation membrane module 11 is supplied not only to the primary side 43 of the second separation membrane module 12 but also to the secondary side 44.

In the second branch pipe 7, the non-permeating gas of the first separation membrane module 11 is reduced in pressure by the pressure reducing valve 21 to a pressure close to the pressure of the secondary side 44 of the second separation membrane module 12, and the flow rate of the gas supplied to the secondary side 44 is adjusted by the second dilution gas flow control valve 24.

To increase the hydrogen concentration on the secondary side 34 of the first separation membrane module 11, it is necessary to ensure that the flow rate of the supply gas is such that the hydrogen concentration at the outlet of the primary side 33 of the first separation membrane module 11 does not decrease significantly. If the supply gas flow rate is low, the methane concentration increases at the outlet of the primary side 33 of the first separation membrane module 11 as hydrogen permeates, and the amount of methane permeated to the secondary side 34 increases, decreasing the hydrogen concentration on the secondary side 34. If the supply gas flow rate is increased to maintain a high hydrogen concentration on the secondary side 34, the amount of hydrogen passing through the first separation membrane module 11 as a non-permeating gas increases, and the recovery rate, which is the ratio of the amount of hydrogen extracted to the secondary side 34 to the amount of supply gas, decreases.

In order to improve the recovery rate, a second separation membrane module 12 is installed to separate hydrogen from the non-permeable gas that has passed through the first separation membrane module 11. The second separation membrane module 12 allows hydrogen to permeate to the secondary side 44, and the amount of hydrogen in the non-permeable gas that passes through the second separation membrane module 12 and is discharged from the hydrogen separation system 1 through the second non-permeable gas pipe 9 is significantly reduced. The permeable gas to the secondary side 44 passes through the second permeable gas pipe 6, is boosted by the booster 30 to a pressure higher than that in the first supply pipe 3, and is merged with the mixed gas in the first supply pipe 3 and is supplied to the first separation membrane module 11 as a recycled gas. In this way, hydrogen is separated from the gas that has permeated the second separation membrane module 12 again by the first separation membrane module 11.

At this time, if the amount of hydrogen permeating the second separation membrane module 12 is increased, the amount of hydrogen discharged from the hydrogen separation system 1 decreases, further improving the recovery rate. As mentioned above, the amount of hydrogen permeation is determined by the partial pressure difference between the hydrogen gas on the primary side and the secondary side. Therefore, if the hydrogen concentration on the secondary side is reduced, the hydrogen partial pressure on the secondary side decreases, the partial pressure difference increases, and the amount of hydrogen permeation increases.

In this embodiment, the second branch pipe 7 is branched from the second supply pipe 4 and supplied as the second dilution gas to the secondary side 44 of the second separation membrane module 12. Since the hydrogen concentration of the gas flowing through the second supply pipe 4 is naturally lower than the hydrogen concentration on the secondary side 44 of the second separation membrane module 12, the gas on the secondary side 44 can be diluted with the second dilution gas to lower the hydrogen concentration. The permeation gas of the second separation membrane module 12 is separated again in the first separation membrane module 11, so there is no problem even if the hydrogen concentration is reduced to some extent. In addition, since the reduction in the hydrogen concentration of the permeation gas can be tolerated to some extent, the separation membrane area of the second separation membrane module 12 can be made larger than the separation membrane area of the first separation membrane module 11, and the amount of hydrogen permeating the second separation membrane module 12 can be increased to further improve the recovery rate.

Here, the recovery rate (unit: %) of component A that constitutes the mixed gas is calculated using the following formula (1).

(Recovery rate of component A)={(Outlet flow rate of mixed gas)×(Outlet concentration of component A)}/{(Inlet flow rate of mixed gas)×(Inlet concentration of component A)}×100 ... (1)
The above formula (1) is applicable to both the case where the component A of the mixed gas exemplified in this embodiment is hydrogen and the case where the mixed gas is composed of other components.

Next, we will explain the results of calculating the gas separation performance of the gas separation system of this embodiment.

Figure 2 shows the results of a trial calculation of the gas separation performance of a gas separation system of a comparative example, that is, when dilution from the second branch pipe is not performed.

In this diagram, the flow rate in the first supply pipe is 100, the hydrogen concentration is 20%, and the methane concentration is 80%. A polyimide membrane with a hydrogen to methane permeation rate ratio of approximately 300 is used for the hydrogen separation membrane. The separation membrane area is the same for the first separation membrane module and the second separation membrane module. The pressure is 1.7 MPaA on the primary side and 0.1 MPaA on the secondary side. The unit of concentration of hydrogen and other substances exemplified in this specification is mol%.

When the dilution shown in this figure is not performed, the amount of gas passing through the second separation membrane module that is recycled is 5.2, the flow rate of the recovered gas is 20.8, the hydrogen concentration is 86.4%, and the recovery rate is 89.7%.

Figure 3 shows the results of a trial calculation of the gas separation performance of the gas separation system of Figure 1. That is, this is the case where the secondary side of the second separation membrane module is diluted at a flow rate of 20.0. The conditions such as the flow rate in the first supply pipe, hydrogen concentration, methane concentration, hydrogen separation membrane permeation rate ratio, separation membrane area, and primary and secondary pressures are the same as in Figure 2.

The gas recycled from the second separation membrane module is 26.4, including the dilution gas flow rate of 20.0. The flow rate of the recovered gas is 22.0, the hydrogen concentration is 87.2%, and the recovery rate has improved to 96.0%. By supplying dilution gas to the secondary side of the second separation membrane module, the amount of hydrogen that permeates the second separation membrane module increases, improving the recovery rate.

Compared to Figure 2, the flow rate and hydrogen concentration of the gas flowing out from the primary side of the second separation membrane module are both lower. This shows that the amount of hydrogen flowing out from the gas separation system is decreasing.

In addition, the hydrogen contained in the non-permeating gas that did not permeate the second separation membrane module can be reduced from 2.6% to 1.0% by diluting it as shown in Figure 3, thereby increasing the methane concentration in the non-permeating gas and enabling it to be supplied to users who require high-concentration methane.

These calculation results are intended to compare the hydrogen separation performance in this embodiment, and the flow rate, pressure conditions, membrane area ratio, etc. are set according to the conditions required for actual operation.

When the second dilution gas is not used, the recovery rate can be improved to the same level as in FIG. 3 by further increasing the separation membrane area of the second separation membrane module 12. However, by using this embodiment, the second separation membrane module 12 can be made smaller, which makes it possible to miniaturize the hydrogen separation system 1 and reduce costs.

In addition, from the viewpoint of supplying high-concentration methane, in other words, from the viewpoint of reducing the hydrogen concentration in the gas flowing out from the primary side of the second separation membrane module 12, it is desirable that the hydrogen separation characteristics of the separation membrane of the second separation membrane module 12 be higher than that of the separation membrane of the first separation membrane module 11.

Second Embodiment
FIG. 4 is a schematic diagram showing a gas separation system according to the second embodiment.

This embodiment differs from the first embodiment in that the first branch pipe 8 branched off from the first supply pipe 3 is connected to the secondary side 34 of the first separation membrane module 11.

By supplying a portion of the supply gas as a dilution gas to the secondary side 34 of the first separation membrane module 11 via the first branch pipe 8, the hydrogen concentration on the secondary side 34 decreases, and the hydrogen partial pressure difference between the primary side 33 and the secondary side 34 increases. As a result, the amount of hydrogen permeating the first separation membrane module 11 increases. Although the hydrogen concentration decreases because the gas permeating to the secondary side 34 is diluted, the configuration of this embodiment can be applied in cases where users do not necessarily use high-concentration hydrogen. Since the same amount of hydrogen permeation can be obtained with a smaller separation membrane area, the first separation membrane module 11 can be made smaller while maintaining the recovery rate, and the hydrogen separation system can be made smaller and costs reduced.

It is desirable to provide the first dilution gas flow rate control valve 25 and the pressure reducing valve 22 in the first branch pipe 8, as in the second branch pipe 7. The first dilution gas flow rate control valve 25, or the first dilution gas flow rate control valve 25 and the pressure reducing valve 22, are also referred to as the "first dilution gas flow rate control section."

Figure 5 shows the results of a trial calculation of the gas separation performance of the gas separation system shown in Figure 4.

In Figure 5, the conditions are the same as in Figure 3, except that dilution on the secondary side of the first separation membrane module is added at a flow rate of 20.0.

Compared to Figure 2, the flow rate of the recovered gas is 38.5, including the dilution gas flow rate of 20.0, and the hydrogen concentration drops to 51.1% due to dilution, but the recovery rate improves to 98.3%. Both the flow rate and hydrogen concentration of the gas flowing out from the primary side of the second separation membrane module are lower. This shows that the amount of hydrogen flowing out of the gas separation system is decreasing.

In addition, the hydrogen content in the gas (non-permeable gas) flowing out from the primary side of the second separation membrane module can be further reduced from 1.0% in the first embodiment to 0.5%, and the methane concentration in the non-permeable gas can be improved to supply high-concentration methane to users who require it.

[Third embodiment]
FIG. 6 is a schematic diagram showing a gas separation system according to the third embodiment.

In this figure, a third separation membrane module 13 is added to the configuration of the second embodiment (Figure 4) in order to significantly improve the hydrogen concentration of the gas to be recovered. The first permeable gas pipe 5 of the first separation membrane module 11 is connected to the primary side 53 of the third separation membrane module 13. The third separation membrane module 13 has a hydrogen separation membrane 17 (third gas separation membrane) that separates the primary side 53 from the secondary side 54, and the non-permeable gas of the third separation membrane module 13 is configured to be returned to the first supply pipe 3 through the third supply pipe 10. The third supply pipe 10 is connected so as to merge with the second permeable gas pipe 6 upstream of the booster 30. The hydrogen separation membrane 17 selectively permeates a specific gas.

As in FIG. 4, the amount of hydrogen permeation can be increased by diluting the permeated gas on the secondary side 34 of the first separation membrane module 11 via the first branch pipe 8, but the hydrogen concentration decreases.

In the hydrogen separation system 1 shown in FIG. 6, the hydrogen contained in the permeable gas of the first separation membrane module 11 can be separated by the third separation membrane module 13 to obtain high-concentration hydrogen.

The separated gas is recovered from the secondary side 54 of the third separation membrane module 13 through the third permeate gas pipe 20. The non-permeate gas of the third separation membrane module 13 contains a large amount of hydrogen. For this reason, the non-permeate gas of the third separation membrane module 13 is returned to the first supply pipe 3 as a recycled gas through the third supply pipe 10, and hydrogen is separated again in the first separation membrane module 11. The third supply pipe 10 is merged with the second permeate gas pipe 6 upstream of the booster 30, so that the gas in the second permeate gas pipe 6 and the third supply pipe 10 can be boosted by a single booster 30.

Figure 7 shows the results of a trial calculation of the gas separation performance of the gas separation system shown in Figure 6.

In Figure 7, a pressure difference is required between the primary and secondary sides of the third separation membrane module, so the secondary side of the first separation membrane module is set to 0.2 MPaA. The separation membrane area of the third separation membrane module is the same as the other modules. The other conditions are the same as in Figure 5.

Compared to Figure 5, the flow rate of the recovered gas is 19.1, and the hydrogen concentration has improved to 98.4% due to separation in the third separation membrane module. On the other hand, the recovery rate has dropped to 94.4%. This is because the amount of recycled gas has increased, which has increased the flow rate of the gas flowing out of the second non-permeable gas piping connected to the primary side of the second separation membrane module, and the hydrogen concentration of the gas supplied to the primary side of the first separation membrane module by the recycled gas has increased, which has resulted in an increase in the hydrogen concentration of the gas flowing out of the second non-permeable gas piping.

Figure 8 shows the results of a trial calculation of the gas separation performance of a gas separation system according to a modified example of the third embodiment.

The difference between this figure and Figure 7 is that there is no first branch pipe that branches off from the first supply pipe that supplies the mixed gas and is connected to the secondary side of the first separation membrane module.

In Figure 8, the flow rate of the recovered gas is 18.7, and the recovery rate is 92.1%. Although these values are lower than those of the configuration in Figure 7, it can be seen that the hydrogen concentration can be maintained at 98.4%. Therefore, it can be said that the modified example shown in Figure 8 can obtain the same hydrogen concentration with a simpler system than that shown in Figure 7.

[Fourth embodiment]
FIG. 9 is a schematic diagram showing the configuration of a gas separation system according to the fourth embodiment.

The difference between this figure and the second embodiment in FIG. 4 is that a signal processing device 50 (control device) is provided to control the opening of the first dilution gas flow rate adjustment valve 25 of the first branch pipe 8.

The control device is composed of a computer equipped with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a storage device such as a HDD (Hard Disk Drive), and a display. The CPU executes a program stored in the HDD to perform calculations and generate control signals.

In FIG. 9, a flowmeter 41 (flow sensor) that measures the flow rate of the supply gas and a concentration meter 42 (concentration sensor) that measures the hydrogen concentration are installed on the first supply pipe 3. The signal from the flowmeter 41 is sent to a signal processing device 50 via a flowmeter signal cable 51, and the signal from the concentration meter 42 is sent to a hydrogen concentration meter signal cable 52. Based on these signals, the signal processing device 50 performs calculations to adjust the opening of the first dilution gas flow control valve 25 of the first branch pipe 8 to an appropriate value, and sends a control signal to the first dilution gas flow control valve 25 via a flow control valve control signal cable 153.

When hydrogen produced using renewable energy such as solar power generation is mixed into the mixed gas main pipe 2, the hydrogen concentration may fluctuate over time. If the hydrogen concentration in the mixed gas main pipe 2 fluctuates, the hydrogen concentration of the gas recovered through the hydrogen separation system 1 will also fluctuate. If the recovered gas is to be used directly without being stored, it may be necessary to maintain the hydrogen concentration at a constant level or higher, depending on the equipment. For this reason, it is desirable to control the hydrogen concentration of the recovered gas to a constant level.

In this embodiment, the flow rate of the first dilution gas (first dilution gas flow rate) flowing through the first branch pipe 8 is adjusted by controlling the opening of the first dilution gas flow rate adjustment valve 25, thereby controlling the hydrogen concentration of the recovered gas (recovered gas hydrogen concentration) flowing out from the first permeable gas pipe 5 to a constant value. If the first dilution gas flow rate is high, the hydrogen concentration of the recovered gas decreases, and if the first dilution gas flow rate is low, the hydrogen concentration of the recovered gas increases. For this reason, the first dilution gas flow rate is controlled based on the hydrogen concentration of the mixed gas flowing through the first supply pipe 3.

Figure 10 is a graph showing the results of a trial calculation of the relationship between the first dilution gas flow rate and the recovered gas hydrogen concentration, with the hydrogen concentration of the gas supplied from the first supply pipe as a parameter in the gas separation system of Figure 9. The horizontal axis represents the first dilution gas flow rate, and the vertical axis represents the recovered gas hydrogen concentration.

In Figure 10, the hydrogen concentration of the gas supplied from the first supply pipe (supply gas hydrogen concentration) is shown as a solid line at 10%, a dashed line at 20%, and a dashed line at 30%. Other than the first dilution gas flow rate, the conditions are the same as those in Figure 5.

As the first dilution gas flow rate increases, the hydrogen concentration in the recovered gas decreases. Also, the higher the hydrogen concentration in the supply gas, the higher the hydrogen concentration in the recovered gas.

For example, as shown in FIG. 10, when the supply gas hydrogen concentration is 10%, the recovered gas hydrogen concentration can be increased to 60% by setting the first dilution gas flow rate to about 4. If the supply gas hydrogen concentration rises to 20%, the recovered gas hydrogen concentration can be increased to 60% by setting the first dilution gas flow rate to about 11. Furthermore, if the supply gas hydrogen concentration rises to 30%, the recovered gas hydrogen concentration can be maintained at 60% by setting the first dilution gas flow rate to about 21. In this way, the recovered gas hydrogen concentration can be controlled by adjusting the first dilution gas flow rate.

In summary, in order to maintain the recovered gas hydrogen concentration at a constant value or within a specified range, as the supply gas hydrogen concentration decreases, the first dilution gas flow rate is controlled to be reduced, i.e., the opening of the first dilution gas flow rate adjustment valve 25 in FIG. 9 is controlled to be reduced, and as the supply gas hydrogen concentration increases, the first dilution gas flow rate is controlled to be increased, i.e., the opening of the first dilution gas flow rate adjustment valve 25 in FIG. 9 is controlled to be increased.

In FIG. 10, the recovered gas hydrogen concentration is controlled to be maintained at a constant value by adjusting the flow rate of the first dilution gas flowing into the secondary side 34 of the first separation membrane module 11, but the present disclosure is not limited to this, and the recovered gas hydrogen concentration may be controlled to be maintained at a constant value or within a predetermined range by adjusting the flow rate of the second dilution gas flowing into the secondary side 44 of the second separation membrane module 12.

In the above embodiment, a configuration is described in which the piping for gas supplied to the primary side is branched and supplied to the secondary side, but a configuration in which the piping for gas flowing out from the primary side is branched and introduced to the secondary side may also be used. This configuration is described next.

[Fifth embodiment]
FIG. 11 is a schematic configuration diagram showing a gas separation system according to the fifth embodiment.

The difference between this figure and FIG. 1 of the first embodiment is that a second non-permeate gas branch pipe 107 is provided instead of the second branch pipe 7 in FIG. 1. That is, the second non-permeate gas pipe 9, which is the pipe for gas flowing out from the primary side 43 of the second separation membrane module 12, is branched and introduced into the secondary side 44. The second non-permeate gas branch pipe 107 is provided with a pressure reducing valve 121 and a second dilution gas flow rate adjustment valve 124.

In this embodiment, as in the first embodiment, by supplying a dilution gas to the secondary side 44 of the second separation membrane module 12, the amount of hydrogen permeating the second separation membrane module 12 can be increased, and the recovery rate can be improved.

Below, we summarize preferred embodiments of this disclosure.

In the gas separation system, a booster is provided downstream of the junction of the first supply pipe and the second permeable gas pipe, or in the second permeable gas pipe.

The second branch pipe is provided with a second dilution gas flow control valve.

The specific gas is supplied to the user through the first permeable gas pipe.

Gas excluding specific gases is supplied to the user via the second non-permeable gas piping.

Furthermore, a first branch pipe is provided that connects the first supply pipe to the secondary side of the first separation membrane module.

The first branch pipe is provided with a first dilution gas flow control valve.

The second dilution gas flow rate adjustment valve includes a pressure reducing valve.

The first dilution gas flow rate adjustment valve includes a pressure reducing valve.

The gas separation system further comprises a third separation membrane module having a third gas separation membrane that selectively permeates a specific gas and separated into a primary side and a secondary side by the third gas separation membrane, a third permeable gas pipe connected to the secondary side of the third separation membrane module, and a third supply pipe provided between the primary side of the third separation membrane module and the second permeable gas pipe or the first supply pipe, and the first permeable gas pipe is connected to the primary side of the third separation membrane module.

A booster is provided downstream of the junction between the first supply pipe and the second permeable gas pipe, or downstream of the junction between the second permeable gas pipe and the third supply pipe in the second permeable gas pipe.

The gas separation system further includes a flow sensor that measures the flow rate of gas flowing through the first supply pipe, a concentration sensor that measures the concentration of a specific gas flowing through the first supply pipe, and a control device that receives signals from the flow sensor and the concentration sensor and adjusts the opening of the first dilution gas flow control valve based on the signals.

The control device adjusts the opening of the first dilution gas flow control valve so as to maintain the concentration of the specific gas supplied to the user from the first permeable gas pipe within a predetermined range.

Finally, we will explain the effects of the gas separation system disclosed herein.

According to the present disclosure, the amount of specific gas permeated through the first separation membrane module and the second separation membrane module increases, thereby improving the recovery rate of the specific gas. Furthermore, if the amount of specific gas permeated is the same, a smaller membrane area is sufficient, and the module can be made smaller, making it possible to reduce the cost of the separation system. By improving the recovery rate of the specific gas, the concentration of the specific gas in the non-permeating gas can be reduced, and non-permeating gas with a low concentration of the specific gas can be supplied to users of the non-permeating gas.

1: Hydrogen separation system, 2: Mixed gas main pipe, 3: First supply pipe, 4: Second supply pipe, 5: First permeable gas pipe, 6: Second permeable gas pipe, 7: Second branch pipe, 8: First branch pipe, 9: Second non-permeable gas pipe, 10: Third supply pipe, 11: First separation membrane module, 12: Second separation membrane module, 13: Third separation membrane module, 15, 16, 17: Hydrogen separation membrane, 20: Third permeable gas pipe, 21, 22 , 121: Pressure reducing valve, 23: Supply gas flow rate adjustment valve, 24, 124: Second dilution gas flow rate adjustment valve, 25: First dilution gas flow rate adjustment valve, 30: Booster, 33, 43, 53: Primary side, 34, 44, 54: Secondary side, 41: Flow meter, 42: Concentration meter, 50: Signal processing device, 51: Flow meter signal cable, 52: Hydrogen concentration meter signal cable, 107: Second non-permeable gas branch pipe, 153: Flow rate adjustment valve control signal cable.

Claims (13)

A first separation membrane module having a first gas separation membrane that selectively permeates a specific gas and is configured to be separated into a primary side and a secondary side by the first gas separation membrane;
a second separation membrane module having a second gas separation membrane that selectively permeates the specific gas and is configured to be separated into a primary side and a secondary side by the second gas separation membrane;
A first supply pipe for supplying a mixed gas containing the specific gas to a primary side of the first separation membrane module;
A second supply pipe connecting a primary side of the first separation membrane module and a primary side of the second separation membrane module;
A first permeate gas pipe connected to a secondary side of the first separation membrane module;
a second non-permeate gas pipe connected to the primary side of the second separation membrane module;
a second permeation gas pipe provided between the secondary side of the second separation membrane module and the first supply pipe, for supplying the gas that has permeated the second gas separation membrane to the first supply pipe;
a second branch pipe connecting the second supply pipe or the second non-permeate gas pipe to a secondary side of the second separation membrane module. The gas separation system according to claim 1, wherein a booster is provided downstream of the junction of the first supply pipe and the second permeable gas pipe, or in the second permeable gas pipe. The gas separation system according to claim 1, wherein the second branch pipe is provided with a second dilution gas flow control valve. The gas separation system according to claim 1, wherein the specific gas is supplied to a user through the first permeable gas piping. The gas separation system according to claim 1, wherein gas excluding the specific gas is supplied to a user via the second non-permeable gas piping. The gas separation system according to claim 1, further comprising a first branch pipe connecting the first supply pipe and the secondary side of the first separation membrane module. The gas separation system according to claim 6, wherein the first branch pipe is provided with a first dilution gas flow control valve. The gas separation system of claim 3, wherein the second dilution gas flow rate control valve includes a pressure reducing valve. The gas separation system of claim 7, wherein the first dilution gas flow control valve includes a pressure reducing valve. a third separation membrane module having a third gas separation membrane that selectively permeates the specific gas and is configured to be separated into a primary side and a secondary side by the third gas separation membrane;
a third permeate gas pipe connected to the secondary side of the third separation membrane module;
A third supply pipe is provided between the primary side of the third separation membrane module and the second permeation gas pipe or the first supply pipe,
The gas separation system according to claim 1 , wherein the first permeate gas pipe is connected to a primary side of the third separation membrane module. The gas separation system according to claim 10, wherein a booster is provided downstream of the junction between the first supply pipe and the second permeable gas pipe, or downstream of the junction between the second permeable gas pipe and the third supply pipe in the second permeable gas pipe. a flow rate sensor that measures a flow rate of the gas flowing through the first supply pipe;
a concentration sensor that measures the concentration of the specific gas flowing through the first supply pipe;
8. The gas separation system according to claim 7, further comprising a control device that receives signals from the flow rate sensor and the concentration sensor and adjusts an opening degree of the first dilution gas flow rate adjustment valve based on the signals. The gas separation system according to claim 12, wherein the control device adjusts the opening of the first dilution gas flow control valve so as to maintain the concentration of the specific gas supplied to the user from the first permeable gas pipe within a predetermined range.

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